The Atacama Desert is a plateau in South America covering a 1,000 kilometre (600 ml) strip of land on the Pacific coast, west of the Andes mountains. It lies mainly in northern Chile. It is the driest non-polar desert in the world. The Atacama Desert proper is estimated to occupy 105,000 square kilometres (41,000 sq mls). Roughly another 20,000 square kilometres (7,722.6 sq mls) can be added if the barren lower slopes of the Andes are included. Most of the desert is composed of stony terrain, salt lakes, sand, and highly viscous felsic lava. Among the volcanic craters of El Tatio, sitting at an altitude of 4,200 metres (13, 779.5 ft), geysers and hot springs are a feature of the landscape.
The Atacama Desert is almost completely sheltered from moisture bearing air currents by the high mountain ranges it lies between and has gained a reputation as the driest place on earth. The average rainfall is about 15 millimetres (0.6 in) per year, although some areas receive even less. It has been this way for millions years, making it the oldest continuously arid region on earth. On rare occasions, however, torrential rain can fall, most recently on 25 March 2015 when torrential rain caused an avalanche of mud and water to tear down from the Andes submerging towns, and leaving 25 people dead.
In part of the Atacama the soil is considered similar to that on Mars and this area is used by NASA to test instruments for future Mars missions, particularly those used to pick up signs of life. It has been used as a location for filming scenes set on Mars. In another area of the Atacama lies the Valley of the Moon which is said to look like the surface of the moon. Due to the area’s remoteness and clear, dry air it is one of the best places in the world for astronomical observation.
In spite of the environmental limitations of the area a rich variety of flora has evolved, mostly low growing herbs and flowers. One of these is the llareta, which only grows at high altitudes and whose dense form is similar to a pillow 3 to 4 metres (10 to 13 feet) thick. It has a growth rate of about 1.5 centimetres (0.6 in) a year, meaning that many plants are over 3,000 years old. Where humidity is sufficient small native trees can be found. Some cactus species and other succulents thrive in the dry conditions.
Few animal species inhabit the region. A number of reptiles can be found in the desert, and guanacos and vicunas, both members of the camel family, can be found in some less extreme areas. Some birds enjoy the conditions. Humboldt penguins live along the coast, nesting in desert cliffs overlooking the ocean; and on the salt flats Andean flamingos dine on algae.